Acousto-optic imaging spectropolarimetry for remote sensing.

We review the operating principles of noncollinear acousto-optic tunable filters (AOTF's), emphasizing the use of two orthogonally polarized beams for narrow-band imaging. Spectral characterization and spectral broadening measurements of commercially available AOTF's agree with theoretical predictions and reveal difficulties associated with imaging noncollimated light. An AOTF imaging spectropolarimeter for ground-based astronomy that uses CCD's has been constructed at NASA Goddard Space Flight Center. It uses a TeO(2) noncollinear AOTF and a simple optical relay assembly to produce side-by-side orthogonally polarized spectral images. We summarize the instrument design and initial performance tests. We include sample spectral images acquired at the Goddard Geophysical and Astronomical Observatory.

Is there any chlorine monoxide in the stratosphere?

A ground-based search for stratospheric chlorine monoxide was carried out during May and October 1981 with an infrared heterodyne spectrometer in the solar absorption mode. Lines due to stratospheric nitric acid and tropospheric carbonyl sulfide were detected at about 0.2 percent absorptance levels, but the expected 0.1 percent lines of chlorine monoxide in this same region were not seen. Stratospheric chlorine monoxide is less abundant by at least a factor of 7 than is indicated by in situ measurements, and the upper limit for the integrated vertical column density of chlorine monoxide is 2.3 x 10(13) molecules per square centimeter at the 95 percent confidence level. These results imply that the release of chlorofluorocarbons may be significantly less important for the destruction of stratospheric ozone than is currently thought.

Diode laser-CO(2) laser heterodyne spectrometer: measurement of 2sQ(1,1) in 2nu(2) - nu(2) of NH(3).

A carbon dioxide laser has been coupled with a tunable diode laser spectrometer for heterodyne calibration of molecular spectra. The output of the diode laser is measured to be 10-15 MHz wide and is stable to within +/-2 MHz. The frequency of the 2(s)Q(1,1) transition in the 2nu(2) - nu(2) band of ammonia is measured to be 949.44746(24) cm(-1).

Precision measurements of NH(3) spectral lines near 11 microm using the infrared heterodyne technique.

Absolute line-center frequencies for eleven lines of ammonia in near coincidence with CO(2)-laser transitions have been determined to accuracies of +/-3 MHz by infrared heterodyne detection. These results were obtained by heterodyning a blackbody with a stable, grating-tuned CO(2) gas laser. A discussion of the apparatus and method of calculation, including error analysis, is presented. With these accurately determined line-center positions, the ammonia molecule will be a useful secondary-frequency standard for diode-laser spectroscopy in the 11-microm wavelength region.